Carburizing procedure



March 14, 1961 w. E. ENGELHARD CARBURIZING PROCEDURE Filed Nov. 5, 1959INVEN TOR. E 5 N6 1 644R .2 BY

United States Patent w 2,975,082 CARBURIZING. PROCEDURE William E.Engelhard, Apalachin, N.Y. Temperature Processing Co. Inc., 228 RiverRoad, North Arlington,

Filed Nov. 5, 1959, Ser. No. 851,066 1 Claim. I (Cl. iris-16.5

This invention relates to the art of carburizing metallic partsinitially having a low carbon content, to increase such content at andslightly below the surface and thereby enhance the surface hardeningcharacteristics of such parts.

The degree of case hardening desired varies according to use to be madeof the parts; hence it is essential, for practical purposes, that thecar-burizing procedure .be adaptable to the requirements of various,uses. Various procedures heretofore proposed to attain this objectiveare objectionable as they are not adapted to practical carburizing ofparts to precise degrees of case depth and within precisely controlledranges. Many .carburizing plants will not undertake to do casehardening, for example, of two to three thousandths of an inch, or tocontrol case hardening within a thousandth of an inch. That is sobecause, generally, carburizing is performed concurrently with theheating of the parts to the critical carburizing temperature, some partsof the load reaching this temperature before others, making it difiicult.to control the procedure and degree of carburizing. There isthe furthercomplication that while heating to carburizing temperature, the parts.become carburized or decarburized to a degree that is difficult tocalculate for shallow cases. As a result the finished product (even ifan attempt is made to compensate for'the varying degree of carbon gain)will not be carburized to precisely the depth desired. Control. ofprecise degrees of cartical matter, be attained. Under the previouspractices, burization, under such procedures, could not, as a practicalmatter, be attained. Under the previous practices, where carburizationoccurs while work is approaching carburizing temperature, as in moststandard practices, the degree of carburization cannot be accuratelycontrolled by the operator; consistently uniform results cannot beattained, unless the case depth required (.010" or more for example) isso great that the effect of carburizing during the initial (coming toheat) part of the cycle is relatively insignificant.

1 The procedure of this invention enables the carburizing of parts toprecisely the predetermined desired degree consistently commercially-forexample .0002" to .010"; the parts in batches thus treated arecarburized to the predetermined desired degree, uniformly and withoutrisk of over or under-casing.

The foregoing and other advantages and objects of the invention willbecome apparent from the description below and from the accompanyingdrawings, wherein:

Fig. l is a vertical, partly fragmentary, sectional view of acarburizing procedure embodying the invention,

Fig. 2 is a fragmentary, elevational view, illustrating parts used forconnection of a source of gas19 with the valve 21 and pipe 22 of Fig. l,v

Fig. 3 is a fragmentary, vertical, sectional view, showing anothersource (19a) of gas for connection with valve 21 to pipe 22, said source19a in'turn originating in gas flowing through pipe 35 and bubbledthrough tank Fig. 4 is a partly fragmentary, elevational view of partsused for connection of another source of gas (19b) with valve 21 forpipe 22 and Fig. 5 is a partly fragmentary, elevational view, showingparts carburizedspursuant to the invention about to be rapidly quenchedand cooled.

Pursuant to the method of this invention, the batch of steel parts to becase hardened is initially placed on a plate 10 or in aholder or bell 11(which may be a perforated member such as an inverted basket or the likepositioned on plate 10) or on a spacer 12, which, in turn, is positionedon plate 10. The parts are thus positioned in a chamber 13 of a furnace14; the chamber may be closed by a suitable cover 15 and provided withelectrical or other heating means 16, thereby directing heat inwardlyfrom the side walls of the chamber 13. Thermocouples 17 may bepositioned at various points in the mass of parts being treated, asshown in Fig. l and connected, as by the wires 18, with temperaturereading instruments so that the operator may control the heating means16 (or to automatic control means) to heat the parts to their criticaltemperature at which they becomereceptive to rapid carbon surfacepenetration, continuing such heating until all of the parts have reachedthat temperature. The procedure of the present invention enablescarburization to be successfully performed commercially of batches ofparts with consistently uniform results and within ranges not possiblein prior procedures.

As a practical example of an application of this invention (and withoutlimiting the invention thereto), the parts may be thus heated. to about1,350 to 2,000 degrees F. for about one hour. While the parts are thusheated, a gas neutral to the initial carbon content of the parts ispassed under pressure onto the parts, also excluding the air atmosphere.The source of gas may, as shown in Fig. 2, be a source of gas with nocarburizing potential, from a source 19 connected, as by a coupling 20,to a valve 21 and thence through a pipe 22 passing through an aperture23 of an inverted, U'-shaped imperforate shield or bell 2.4 assembledover the parts, and onto the plate 10. The lower end of pipe 22 may bewelded as at 25 to the plate 10; said pipe is preferably provided I withapertures 26 spaced from the plate ,10 a lesser] distance than. theheight of the shield so that said, gas will pass through the pipe 22fromthe source 19,, through the apertures 26 and onto the parts in theshield 24 and thence between the shield and the plate 10. The

plate 10 may be of larger dimensions than the shield 24 and may becircumferentially upturned as at 27 to form, with the lower end of theshield, arestricted passage for such gases in escaping from the shield.In practice, the actual space between the upturned circumferential edge27 of the plate-10 and the shield may be I i steel parts and avoidsoxidation as the 'parts are brought up to their critical temperature.When heating of the parts has been continued sufficiently to assure thatall of i the parts are brought up to their desired critical temperatureand that they are uniformly at that temperature, the source 19 is cutoff, as by the valve 21, and the valve 1 30 opened to admit an activecarburizing gas, such as f methane, propane, or any other carbonaceousgas, from source 32, through coupling 31 and valve 30 to the p'ipe 3 22and thence through the apertures v26 and-ontothe parts, for a muchshorter period of time-for example, from one to ten minutes. Thecarburizing gas may thus be applied for a fraction of the timepreviously-required (by controlling the rateof flow of gas from source32 through valve 30) and then the assembly is ready for quenching. Bycontrolling the time andquantity-ofgas from source '32 thus swept overthe parts in shield 124 in this carburizing stage ofthe procedure of theinvention, the precise depth of caseofthe parts thus treated may beaccurately controlled within ranges heretofore not practical orcommercially :possible of attainment. Case hardening to precisely thedesired degree is commercially consistently attainedpursuant totheinvention. It is possibletocase-harden parts from .0002 to .010" as apractical matter and to obtain uniformly consistent results incommercial practice, pursuant to the invention.

After the carburizingprocedure, the pipe 22, the plate 10 and assemblythereon abovedescribed may be lifted from the chamber 13 ofthe furnace(as by cable 28) and cooled by suitable means, as by being immersed inthe tank 29 for rapid quenching.

The parts may be suitably formed to facilitate assembly or disassembly.To that end, holder 11 may be provided with an aperture at the topthereof enabling it .to be slidably disposed on the pipe 22; as abovementioned, the shield 24 is provided with aperture 23 at the top thereof(and may have a sealing gasket 23) to freely slidably dispose it on thepipe 22.

After completion of the procedure of carburization, pursuant to theinvention, the pipe 22 may be separated, as at 33 (Fig. 1) from the pipe34 and valves 21 and30, and the holder 11 and batch of parts thereinremoved from the pipe 22. A holder 11 and new batch of parts therein andshield 24 may be repositioned in the assem- "bly -as in Fig. 1 forrepeating the procedure of themvention. The perforated holder 11, shield24 and asso- =ciated features thereof and of the assembly shown in Fig.1 promote the uniform heating and subsequent uniform cooling of each ofthe parts in the batch being treated pursuant to the invention.

This application is a continuation in part of my copending application,Serial No. 739,039, 'filed June 2,

1958, and now abandoned; Figs. 1, 2 and 5 of present applicationcorresponding generally to Figs. 1 and2 of said application.

I have found that, for some work normally troublesome to carburizeuniformly because of varying carbon content or because of containedimpurities such as sulfur or lead, or to salvage work previouslyover-cased, excellent results may be obtained if, instead of using thegas source illustrated in Fig. 2 of this application as a source of dryneutral non carburizing hydrogen gas, a source 19b (Fig. 4) ofdecarburizing gas e.g. hydrogen having a high moisture content is used.Said hydrogen gas of high dew point may either be provided as such gasflowing through the pipe 1% of Fig. 4 or it may initially be dryhydrogen or mixture of nitrogen and hydrogen passed through the pipe 35(Fig. 3) coupling 35 and valve 37, through the pipe 38 and bubbledthrough water in the tank 39, emerging as a gas of high moisture contentwhich is then passed as through a suitable coupling (as 20 and valve 21of Pig. 2) with the pipe 22 of the apparatus. I

The carburizing procedure otherwise followed pursuan to the invention inthe use of the forms shown in Figs. '3 and 4 and above described followsthat described in connection with Figs. 1, 2 and 5.

l have found that, with the use of hydrogen or dissociated ammonia witha high moisture content, carbon, sulfur and other impurities may bescavenged initially, where desirable, thus providing a uniform materialfor precise carburization and eliminating interference with theabsorption of carbon in the carburizing procedure to follow.

tank 29 (water, oil-orother liquid).

temperature of the parts. cooling of the .parts, the assembly may beremoved from Far greater accuracy.is..attained, pursuant tothis invention, than in prior attempts :to carburize parts which are at varyingtemperatures. As above noted, pursuant to the invention, the parts areheated, as shown in Fig. 1, in the furnace 14 and brought up to thatpredetermined degree of heat at whichsit isfdesired to carburize them;heating of the parts at that temperature is continued (while the partsarercontinuously .washe'dby the neutral ,gasirom source 19, 19a .or .191,for .sufiicient time to insure :that all of 1the;.parts will havemnifornily .attained the precise desired predetermined temperature.'When the parts, through sufiiciently continued heating, uniformly reachthe'prccise desiredpredetermined temperature, the flow of gas :fromsource .19 (19mm 19b) is discontinued, as by shutting valve 21, andvalve 30 opened for the precise time required for carburizing said partsto case harden them to the precise desired degree; valve 30 is then shutoff.

Valve 21 may be turned on again and the assembly of Fig. 1 thenliftedout of the furnace and-left tolcool in air before the case is-set,where, for example, .it is .desired to perform machining or otheroperations before the caseis set on all surfaces of the-parts. Where,after the carburizing procedure of Fig. 1 has been completed, it isdesiredto attain case setting of allsurfaces .of the parts,the-assembly'may be immersed in a liquid 35 in The liquid is preferablyunheated so as to be normally at about .room

temperature (or at substantially lower than boiling temperatures')quenching liquid, shield 24 willtend to move downwardly On immersion ofthe assembly in such more slowly and stay above the assembly 10, 1'1,12; additionally the parts will boil and generate gases on immersion inthe'liquid quenching medium 35; gases'will thus be generatedand willflow .upwardly in the shield 24 andhold said shield away from the parts.The pipe '22 may have stop means to limit movement of shield 24 awayfrom the parts and to keep the shield under the surface-of liquid 35.The quenching medium'thus fully immerses the parts and rapidly quencesthem univolume of liquid medium 35 inside the shield, which fraction isphysically adjacent and therefore close to the After such .second phase.slow

tank 29.

The invention, while not limited thereto, has provento be highly usefulin connection with treatment of ferrous 'parts.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

The method of treating steel parts 'to increase their surface carboncontent to an accurately predetermined extent, comprising enclosing saidparts while spaced from oneanother in a furnace, with heating meanslining side walls thereof, while held in a perforated bell posia flow ofpressurized gas, neutral to the initial carbon content of said parts,with a dew point nothigher than 40" F., to inside the top portion ofsaid imperforate bell, through said'perforated bell, and under thebottom edge of said imperforate bell, whereby the original carboncontent of the steel parts is not decreased, then while stillmaintaining said parts at said uniform temperature, substituting anactive carburizing gas for said 5 neutral gas for an accuratelypredetermined period of time of fi'om one to ten minutes, to therebycase harden said parts to a desired extent between .0002" and .010" indepth and, after treatment in said carburizing gas, rapidly cooling saidsteel parts by immersion in a quenching liquid.

References Cited in the file of this patent UNITED STATES PATENTS OlsenJuly 31, 1923 6 Machlet June 4, 1935 Saives Mar. 25, 1941 Cope July 4,1950 Besselman et al. June 25, 1956 Tauber July 8, 1958 OTHER REFERENCESJohnson: Metal Working and Heat-Treatment Manual, vol. III, pages 51 and155. Library Call No. TS 205

